“Two water bottle caps act as the knobs for the etch a sketch and the guts of an old roller ball USB mouse have been re purposed to control the PC. An old mouse already has two sets of rollers, one for left-right and one for up-down. These normally press against the ball to detect the mouse movement. A slotted disk on the roller spins between an LED and opto sensor pair to detect the rotation of the knob. I have extracted these roller and sensor arrangements and put them on the left and right of the screen. The left and right clicks have also been extended and put behind each knob.”